Field of the Disclosure
This application relates to time synchronization and more particularly to backup time synchronization in wireless communication networks.
Description of the Related Art
The current time synchronization design for 4G Long Term Evolution (LTE) networks utilizes satellite based signals, e.g., Global positioning System (GPS) or Global Navigation Satellite System (GNSS), to provide timing signals for synchronization and clock synthesis of fundamental radio frequencies. LTE base stations (eNodeBs), also referred to herein as access points, have their own GPS antennas to achieve GPS synchronization. But GPS signals are subject to interruption from, e.g., storm damage to antennas from wind and/or lightning, or even GPS jamming or other interference. If the GPS signal is lost, the LTE eNodeB will lose its time synchronization. Typical eNodeBs have the capability to maintain an accurate time reference for some amount of time after a synchronization signal failure, e.g., for up to a few hours or even up to a day. After that, once eNodeB is out of synchronization, LTE services will be lost.
In order to provide high quality service to customers, telecommunication operators typically utilize a backup (second priority) time synchronization source. A typical approach is to use the operators' 3G network, such as the Radio Network Controller's (RNC's) time clock as the backup time synchronization source. Although such an approach does provide a backup, the RNC backup approach has limitations since the second time synchronization frames are carried from the RNC over the backhaul and the accuracy of the backup clock could be degraded due to long distance transmission. Further, if the backhaul has an outage, the eNodeB will lose the backup time synchronization source. Another potential troublesome scenario is that if an LTE eNodeB and Universal Mobile Telecommunication System (UMTS) Radio Network Controller (RNC) uses different Internet Protocol (IP) address plans, such as IPv6 for LTE eNodeB, while the UMTS RNC remains IPv4, then it becomes impossible for LTE eNodeB to use the RNC as a backup time synchronization source.